Always clear dest in SkBitmap::copyTo's draw path

https://codereview.chromium.org/26268003/



git-svn-id: http://skia.googlecode.com/svn/trunk/src@11697 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/core/SkBitmap.cpp b/core/SkBitmap.cpp
index 1d1cc0a..434c817 100644
--- a/core/SkBitmap.cpp
+++ b/core/SkBitmap.cpp
@@ -1119,10 +1119,9 @@
             }
         }
     } else {
-        // if the src has alpha, we have to clear the dst first
-        if (!src->isOpaque()) {
-            tmpDst.eraseColor(SK_ColorTRANSPARENT);
-        }
+        // Always clear the dest in case one of the blitters accesses it
+        // TODO: switch the allocation of tmpDst to call sk_calloc_throw
+        tmpDst.eraseColor(SK_ColorTRANSPARENT);
 
         SkCanvas canvas(tmpDst);
         SkPaint  paint;